Inventive concepts described herein relate to an image sensor, and more particularly, relate to an image sensor supporting various operating modes that make it possible to improve the performance of an analog-to-digital converter (ADC).
The use of a mobile device such as a smartphone, a tablet personal computer (PC), a digital camera, an MP3 player, or an e-book reader continues to increase. To photograph an image, at least one image sensor is mounted on most mobile devices. Image sensors may be implemented, for example, as a charge coupled device (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor, for example.
Compared with a CMOS image sensor, a CCD image sensor has a low noise and an excellent image quality. However, a CMOS image sensor provides for simple and varied scanning and operation. Additionally, a signal processing circuit may be integrated in a single chip with a CMOS image sensor, thereby enabling miniaturization of a product. And, because a CMOS image sensor is compatible with CMOS process technology, the unit cost of production is reduced. Because of low power consumption, a CMOS image sensor is easily applied to a mobile device.
As the resolution of pixels constituting an image sensor increases and as an image sensor is miniaturized, a shared type of pixel array in which a plurality of transmission transistors share the same floating diffusion (FD) area is widely used. In the case of an image sensor using the shared type of pixel array, one analog digital converter generally processes a sense voltage outputted from pixels connected to one column. However, due to a structural feature that a floating diffusion area is shared therewith, all analog digital converters are not used while processing an image and this reduces the operating speed of an image sensor. Accordingly, it is important to improve the operating speed of an image sensor using a shared type of pixel array in which a plurality of transmission transistors shares the same floating diffusion area.